In order to use powder in various applications, there is known a technology of covering the powder with another material to add a new function thereto. For instance, in existing one-component color magnetic toner or color magnetic ink, on magnetic base particles having the magnetism such as iron powder, a coloring layer is disposed to form. In order to obtain a clear color image with the one-component color magnetic toner or color magnetic ink, the magnetic toner or magnetic ink itself has to be colored with a brilliant color. However, since particles of a magnetic material that becomes a base material thereof are generally colored black, when a coloring layer is directly disposed on a surface thereof, as a whole, a dark color results.
On the other hand, the inventors have proposed a method of rendering powder white, in which on a surface of a base particle, under application of ultrasonic, a metallic silver film is formed, and, owing to the reflectivity of the film, powder is rendered white (for instance, patent document 1). The powder provided with the above-cited metallic silver film can reflect all incident light to be able to render the powder white. It is suggested that thus obtained white powder can be made into magnetic toner or ink, or when a surface of the white powder is provided with a coloring layer, brilliantly colored color magnetic toner or ink can be produced.